Pressure sensitive adhesive film overlamination

ABSTRACT

There is disclosed an overlaminating adhesive film comprising a transparent film, an adhesive layer and a release material successively laminated in this order, wherein said release material has a surface contacting with the adhesive layer, said surface having a centerline average surface roughness of 0.5 μm or lower; an adhesive forming said adhesive layer has a pH of 7.2 to 8.5 in a solution state before applied, and is an acrylic emulsion-type adhesive having an average particle size of 200 nm or smaller; and a monomer component used for production of said adhesive includes an alkoxysilane group-containing unsaturated monomer in which each alkoxy group has 1 to 4 carbon atoms, but includes no hydroxy-containing unsaturated monomer. The overlaminating adhesive film of the present invention exhibits a good water resistance and is free from deterioration in its transparency due to lifting or bubbles when laminated on an adherend.

TECHNICAL FIELD

The present invention relates to an overlaminating adhesive film, andmore particularly to an overlaminating adhesive film having a good waterresistance and being free from deterioration in its transparency due tolifting and bubbles when laminated over an adherend, which is capable ofpreventing an ink-jet printed surface over which the film was laminated,from suffering from ink bleeding even when the printed surface isallowed to stand under humidified conditions.

BACKGROUND ARTS

Overlaminating adhesive films have been used to protect a printedsurface produced by thermal transfer printing, ink-jet printing,offset-printing, letterpress printing, gravure printing, etc., fromdamages by water, sunlight, scratches, etc. The overlaminating adhesivefilms generally comprise a surface base material in the form of atransparent film, a release material and an adhesive layer sandwichedtherebetween. The release material is peeled off from the films uponuse.

The adhesives used in the overlaminating adhesive films include variousadhesives of an emulsion type, a solvent type, a solvent-free type, etc.which are made of rubber-based, acrylic or vinyl ether-based compounds.Among these adhesives, the acrylic adhesives are more suitably usedbecause the adhesives of this type are excellent in weather resistance,peeling stability with time and transparency. In particular, specialattention has been recently paid to emulsified acrylic adhesives sincethe adhesives contain no organic solvent harmful to human bodies and,therefore, are favorable to environments (for example, refer to JapanesePatent Application Laid-open Nos. 2001-240819 and 2002-80809).

However, in general, the emulsion-type adhesives are considerablydeteriorated in water whitening resistance and water adhesion resistanceas compared to those of the solvent type adhesives. Also, when the aboveacrylic emulsion-type adhesive is used to produce an overlaminatingadhesive film by a so-called transfer-coating method in which theadhesive is applied on a release material and then a transparent film islaminated over the adhesive, it is required that an additive forimproving the wettability such as surfactant is added to the adhesive inorder to enhance a wettability of the adhesive to the release material.The addition of the additive, however, causes deterioration in waterresistance of the resultant adhesive film. In particular, in the casewhere the overlaminating adhesive film is laminated over an ink-jetprinted surface, there arises such a problem that the printed surfacesuffers from ink bleeding when preserved under humidified conditions.

DISCLOSURE OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide an overlaminating adhesive film having a high water resistancewhich is capable of preventing an ink-jet printed surface over which theadhesive film is laminated, from suffering from ink bleeding even whenthe printed surface is preserved under humidified conditions,notwithstanding the adhesive film is produced by any of a direct coatingmethod of directly applying an acrylic emulsion-type adhesive on atransparent film and then laminating a release material on the adhesive,and the above transfer coating method.

As a result of extensive researches for achieving the above object, thepresent inventors have found that the above problems have been overcomeby the following specific overlaminating adhesive film:

(1) An overlaminating adhesive film comprising a transparent film, anadhesive layer and a release material successively laminated in thisorder,

wherein said release material has a surface contacting with the adhesivelayer, said surface having a centerline average surface roughness of 0.5μm or lower; an adhesive forming said adhesive layer has a pH of 7.2 to8.5 in a solution state before applied; and is an acrylic emulsion-typeadhesive having am average particle size of 200 nm or smaller; and amonomer component used for production of said adhesive includes analkoxysilane group-containing unsaturated monomer in which each alkoxygroup has 1 to 4 carbon atoms, but includes no hydroxy-containingunsaturated monomer;

(2) the overlaminating adhesive film according to the above aspect (1),wherein said acrylic emulsion-type adhesive is prepared byemulsion-polymerizing a mixture composed mainly of an acrylic acid estercontaining a C₄ to C₁₂ alkyl group and a carboxyl-containing unsaturatedmonomer;

(3) the overlaminating adhesive film according to the above aspect (1)or (2), wherein said acrylic emulsion-type adhesive is directly appliedon the transparent film, and then the release material is laminated overthe adhesive; and

-   -   (4) the overlaminating adhesive film according to the above        aspect (1) or (2), wherein said acrylic emulsion-type adhesive        is applied on the release material, and then the transparent        film is laminated over the adhesive.

The present invention has been accomplished on the basis of thisfinding.

PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

The transparent film used in the present invention is not particularlyrestricted as long as the film exhibits a transparency sufficient torecognize information present on an adherend. Examples of thetransparent film include polyolefin films such as polyethylene film andpolypropylene film, polyester films such as polyethylene terephthalate(PET) film and polyethylene naphthalate film, polystyrene films or thelike. Usually, the above transparent films are preferably used in theform of a biaxially oriented film, and may be appropriately selectedaccording to applications thereof. The thickness of the transparent filmmay also be appropriately selected according to applications orconditions thereof, and is preferably in the range of 10 to 100 μm andmore preferably 15 to 50 μm.

One or both surfaces of the transparent film are preferably subjected tocorona treatment and/or anchor treatment. These treatments are effectiveto enhance the adhesion of the transparent film to the adhesive layer aswell as the coatability thereon. However, if these treatments areexcessively conducted, the resultant adhesive film tends to bedeteriorated in transparency. Therefore, these treatments are preferablycarried out to such an extent as not to adversely affect thetransparency of the adhesive film.

The release material used in the present invention must satisfy such arequirement that its surface contacting with the adhesive layer has acenterline average surface roughness of 0.5 μm or lower. When therelease material such as release paper has a low surface smoothness,irregularities present on its surface are directly transferred to theadhesive layer. For this reason, if the centerline average surfaceroughness of the release material exceeds 0.5 μm, there tend to occurdefects such as poor transparency and deteriorated adhesion strength ofthe resultant adhesive film. From these viewpoints, the centerlineaverage surface roughness of the release material is more preferably 0.2μm or lower.

Meanwhile, the above centerline average surface roughness is measured byfixing the release material on a slide glass such that its surfacecontacting with the adhesive layer faces upwards, using a surfaceanalyzer “SAS-2010 Model” available from Meishin Koki Co., Ltd.,according to JIS B 0601-1982.

The materials of the release material used in the present invention arenot particularly restricted as long as they can satisfy the aboverequirements. However, it is required that surface layers of the releasematerial and the adhesive layer are readily peeled from each other at aninterface therebetween. Therefore, the release material may be suitablyselected from those materials produced by laminating a resin film madeof polyethylene, etc., on a kraft paper, a glassine paper, a wood-freepaper, a cast-coated paper, a clay-coated paper, etc.; those materialsproduced by coating a water-soluble polymer such as polyvinyl alcoholand starch on a kraft paper, a wood-free paper, a cast-coated paper,etc., those materials produced by applying a silicone-based releaseagent, etc., onto a film or a synthetic paper made of polyolefins orpolyesters; and the like.

Of these release materials, in view of a less burden to environments,especially preferred are such release papers obtained by applying asolvent-free silicone as a release agent thereonto.

The acrylic emulsion-type adhesive constituting the adhesive layer ofthe present invention is required to exhibit a pH of 7.2 to 8.5 in asolution state before applied. When the pH of the adhesive is less than7.2, particles emulsified in the adhesive is deteriorated in stabilityand, therefore, tends to be agglomerated. The agglomeration of theparticles tends to cause deterioration in mechanical stability of theadhesive upon coating, which results in formation of streaks due to poorcoatability thereof as well as poor film-forming ability and low waterresistance of the dried coating film.

On the other hand, when the pH of the adhesive exceeds 8.5, alkali suchas aqueous ammonia which is added for controlling the pH tends to beinhibited from vaporizing upon drying, so that the obtained adhesivefilm is deteriorated in water resistance.

The pH of the adhesive is preferably controlled to the above specifiedrange by adding weak alkali thereto, more preferably by adjusting the pHusing aqueous ammonia from the viewpoint of simplicity. Meanwhile, whenthe aqueous ammonia is used as alkali and added to the adhesive in sucha large amount that the pH thereof exceeds 8.5, the obtained adhesivefilm tends to release undesired ammonia odor due to residual ammonia.

Also, the acrylic emulsion-type adhesive of the present invention isrequired to have an average particle size of 200 nm or smaller in asolution state before applied. When the average particle size of theacrylic emulsion-type adhesive exceeds 200 nm, the obtained adhesivelayer tends to be deteriorated in water resistance. The average particlesize of the acrylic emulsion-type adhesive may be controlled bypreviously incorporating a surfactant into the reaction system. As theamount of the surfactant added to the reaction system increases, theaverage particle size of the acrylic emulsion-type adhesive can bereduced. Usually, an optimum amount of the surfactant added may beappropriately selected according to kind thereof.

Meanwhile, in the present invention, the average particle size of theacrylic emulsion-type adhesive was measured as follows. Namely, a dilutedispersion prepared by diluting the acrylic emulsion-type adhesive intoa concentration of 100 ppm with water, is measured by a light scatteringmethod using “NICOMP Model 370” available from Particle Sizing Systems,Inc.

The monomer component used for producing the acrylic emulsion-typeadhesive of the present invention is required to contain an alkoxysilanegroup-containing unsaturated monomer. When such a monomer is containedin the monomer component, the obtained adhesive is enhanced in cohesiveforce after coating, and irregularities present on the surface of therelease material are hardly transferred to the adhesive. As a result,there can be attained such an effect that the obtained adhesive film isinhibited from being deteriorated in transparency.

The alkoxysilane group-containing unsaturated monomer used in thepresent invention is such an unsaturated monomer to which analkoxysilane group is bonded. Examples of the alkoxysilane group includea monoalkoxysilane group, a dialkoxysilane group and a trialkoxysilanegroup. Each alkoxy group contained in the alkoxysilane groups preferablyhas 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms. When aplurality of alkoxy groups are present in one alkoxysilane group, thenumbers of carbon atoms contained in the respective alkoxy groups may bethe same or different from each other. The elements other than alkoxy inthe alkoxysilane group may be a hydrogen atom or an alkyl substituentgroup.

An unsaturated portion of the alkoxysilane group-containing unsaturatedmonomer, namely a portion forming a main chain of the resultant polymeris not limited to particular ones as long as it has a goodpolymerization activity. As the unsaturated portion, there may bepreferably used those having an alkylene skeleton such as ethyleneskeleton (vinyl skeleton), propylene skeleton and butylene skeleton, andmore preferably those having such an alkylene skeleton whose hydrogenatoms are partially substituted with a (meth)acryloxy group.

Specific examples of the alkoxysilane group-containing unsaturatedmonomer include vinylmethoxysilane, vinylethoxysilane,vinyltris(β-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane,γ-methacryloxypropyldimethoxysilane,γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropyldiethoxysilane,γ-acryloxypropyltrimethoxysilane, γ-acrylox γ-propyldimethoxysilane,γ-acryloxypropyltriethoxysilane, γ-acryloxypropyldieth oxysilane or thelike. Of these monomers, especially preferred areγ-methacryloxypropyltrimethoxysilane andγ-methacryloxypropyltriethoxysilane. These monomers may be used singlyor in the form of a mixture of any two or more thereof.

The alkoxysilane group-containing unsaturated monomer may be added in anamount of 0.001 to 5 parts by mass based on 100 parts by mass of wholemonomers used for producing the acrylic emulsion-type adhesive. When thealkoxysilane group-containing unsaturated monomer is used in theabove-specified range, the effect mentioned above can be remarkablyexhibited. Further, in view of the aimed effect, the amount of thealkoxysilane group-containing unsaturated monomer added is morepreferably 0.1 to 1 part by mass.

Also, it is required that the monomer component used for producing theacrylic emulsion-type adhesive contains no unsaturated monomercontaining a hydroxyl group. If an adhesive prepared from the monomercomponent including the hydroxy-containing unsaturated monomer is usedto produce an overlaminating adhesive film, the ink-jet printed surfaceon which the overlaminating adhesive film is laminated tends to sufferfrom ink bleeding when the printed surface is allowed to stand underhumidified conditions. It is considered that the undesirable inkbleeding under humidified conditions is caused by the interactionbetween the hydroxyl group, an ink-receiving layer of the ink-jetprinted surface and the ink, though not clearly known.

On the other hand, when the overlaminating adhesive film using nohydroxy-containing unsaturated monomer according to the presentinvention is laminated over the ink-jet printed surface, the printedsurface is substantially free from ink bleeding even under humidifiedconditions.

The acrylic emulsion-type adhesive used in the present invention is notparticularly restricted as long as it satisfies the above requirements.For example, there may be used acrylic emulsion-type adhesives producedby emulsion-polymerizing a mixture composed mainly of (a) an acrylicacid ester containing a C₄ to C₁₂ alkyl group and (b) acarboxyl-containing unsaturated monomer in the presence of apolymerization initiator, a chain transfer agent, an emulsifier, adispersant, etc., by a known method.

Specific examples of the acrylic acid ester (a) containing a C₄ to C₁₂alkyl group include n-butyl acrylate, isobutyl acrylate, 2-ethylhexylacrylate, n-octyl acrylate, isooctyl acrylate, n-nonyl acrylate,isononyl acrylate, lauryl acrylate or the like. These acrylic acidesters (a) may be used singly or in the from of a mixture of any two ormore thereof.

Specific examples of the carboxyl-containing unsaturated monomer (b)include acrylic acid, methacrylic acid, maleic acid, itaconic acid,fumaric acid, β-carboxyethyl acrylate or the like. Of these monomers,especially preferred are acrylic acid and methacrylic acid. Thesemonomers (b) may be used singly or in the form of a mixture of any twoor more thereof.

The acrylic emulsion-type adhesive of the present invention may alsocontain, in addition to the above alkoxysilane group-containingunsaturated monomer and the components (a) and (b), the otherunsaturated monomers, if required, unless the effects of the presentinvention are adversely affected by the addition thereof. Specificexamples of the other unsaturated monomers include methyl(meth)acrylate, ethyl (meth)acrylate, n-butyl methacrylate, isobutylmethacrylate, 2-ethylhexyl methacrylate, cyclohexyl (meth)acrylate,styrene, α-methyl styrene, acrylonitrile, vinyl acetate, etc., as wellas epoxy-containing unsaturated monomers such as glycidyl (meth)acrylateand methylglycidyl (meth)acrylate, carbonyl-containing monomers such as(meth)acrolein and diacetone acrylamide, methylol monomers such asN-methylol (meth)acrylamide, unsaturated monomers having two or moreunsaturated double bonds such as divinylbenzene, sulfonicgroup-containing monomers such as sodium vinylsulfonate and sodiumstyrenesulfonate, or the like.

The chain transfer agent may be optionally added and serves as acomponent for imparting a pressure-sensitive adhesion force to theadhesive. Specific examples of the chain transfer agent include alcoholssuch as methanol, ethanol and isopropyl alcohol, mercaptans such asdodecyl mercaptan and lauryl mercaptan, or the like.

Various coating apparatuses may be used for applying the above acrylicemulsion-type adhesive, though not limited to particular ones. Specificexamples of the coating apparatuses include known coaters such as a rollcoater, a knife coater, a bar coater, a die coater, an air-knife coater,a gravure coater and a curtain coater.

The amount of the acrylic emulsion-type adhesive applied may becontrolled to the range of 5 to 50 g/m² on the basis of its driedweight. When the amount of the acrylic emulsion-type adhesive appliedlies within the above-specified range, a sufficient adhesion property ofthe resultant film can be obtained and, at the same time, disadvantagessuch as swell-out of the adhesive from the film can be effectivelyinhibited. From the above viewpoints, the amount of the acrylicemulsion-type adhesive applied is more preferably 10 to 30 g/m².

Meanwhile, as the coating method for applying the above adhesive, theremay be used a transfer coating method in which the adhesive is appliedonto the release material such as release paper and then transferredonto the transparent film, or a direct coating method in which theadhesive is directly applied onto the transparent film and thenlaminated on the release material. The overlaminating adhesive film ofthe present invention can be advantageously produced by any of thetransfer coating method and the direct coating method since a wettingagent such as surfactants for enhancing a wettability of the adhesive tothe release material is added to the adhesive in such an amount as notto adversely affect a water resistance thereof.

EXAMPLES

The present invention will be described in more detail by reference tothe following examples, but it should noted that these examples are onlyillustrative and not intended to limit the scope of the presentinvention thereto.

The evaluation methods are explained below

(Evaluation Methods)

1. Transparency

A release paper was peeled off from the respective overlaminatingadhesive films obtained in Examples and Comparative Examples, and eachof the adhesive films was then laminated over a 50 μm-thick PET film toprepare a test specimen having a size of 50 mm×50 mm. The haze of thetest specimen was measured using a turbidity meter “NDH2000” availablefrom Nippon Denshoku Kogyo Co., Ltd.

2. Water Whitening Resistance

The same test specimen as used in the above transparency test wasimmersed in warm water at 60° C. and allowed to stand therein for 3days. Then, the test specimen was taken out of the warm water, and thehaze thereof was measured using the same turbidity meter as used for theabove transparency test.

3. Ink Bleeding Resistance

Images were printed on a color bubble-jet (BJ) printing lustered film“AG-1” as a genuine film available from Cannon Corp., using a printer“BJF-850” available from Cannon Corp. Then, the respectiveoverlaminating adhesive films obtained in Examples and ComparativeExamples were laminated over a printed surface of the lustered film. Thethus obtained laminated film was allowed to stand at 40° C. under arelative humidity of 80% for 2 weeks, and then observed to evaluate anink bleeding resistance thereof according to the following ratings.

A: Identical or less ink bleeding as compared to the case where nooverlaminating adhesive film was used;

B: Much ink bleeding as compared to the case where no overlaminatingadhesive film was used, but still acceptable for practical use;

C: Considerable ink bleeding as compared to the case where nooverlaminating adhesive film was used, to such an extent that designsthereon were severely damaged.

4. Laminating Suitability (Damage of Transparency due to Bubbles)

A Chinese character was screen-printed on a 1 mm-square portion of a 50μm-thick PET film. An overlaminating adhesive film having a size of 50mm×50 mm was laminated over the printed surface of the PET film suchthat bubbles were trapped therebetween. The thus obtained laminated filmwas allowed to stand for 3 days, and then observed by an opticalmicroscope at a magnification of 50 times to evaluate removal of thebubbles therefrom according to the following ratings.

A: A sufficient amount of the bubbles trapped immediately after thelamination were removed so that the film showed a good transparency;

B: A substantial amount of the bubbles trapped immediately after thelamination were removed so that the film showed a good transparency;

C: A some amount of the bubbles trapped immediately after the laminationremained, but the transparency of the film was still maintained as aresult of visual observation; and

D: An almost whole amount of the bubbles trapped immediately after thelamination were unremoved so that the transparency of the film wasseverely damaged.

5. Peel Trace (Orange Peel)

The respective overlaminating adhesive films obtained in Examples andComparative Examples were rolled up by a length of 30 m around a papertube having a diameter of 3 inch, and allowed to stand for 7 days whilemaintaining its rolled state. Thereafter, a core portion of the roll wascut into a test specimen, and the obtained test specimen was attached toa slide glass to measure an image clarity thereof by a lighttransmission method using an image clarity tester “ICM-IDP” availablefrom Suga Testing Machine Mfg. Co., Ltd. (optical comb spacing: 0.5 mm).The larger value of the image clarity indicates a more excellenttransparency of the film. The image clarity value approximatelycorresponds to the following evaluation ratings by visual observation.

90% or higher: Extremely excellent in transparency

85% or higher but less than 90%: Excellent in transparency

75% or higher but less than 85%: Slight orange peel due to adhesive

Less than 75%: Considerable orange peel due to adhesive with damagedtransparency

Example 1 (1) Production of Adhesive

40 parts by mass of ion-exchanged water and 0.2 part by mass of aradical-polymerizable surfactant “AQUARON KH-10” available from Dai-IchiKogyo Seiyaku Co., Ltd., were charged into a polymerization flaskequipped with a stirrer, a thermometer, a reflux condenser and adropping funnel, and heated to 80° C.

Next, a mixture composed of 80 parts by mass of 2-ethylhexyl acrylate,16 parts by mass of methyl methacrylate, 2 parts by mass of acrylic acidand 2 parts by mass of methacrylic acid was mixed with a solutionobtained by emulsifying and dispersing 0.2 part by mass ofγ-methacryloxypropyltrimethoxysilane as an alkoxysilane group-containingunsaturated monomer (“Silicone KBM-503” available from Shin-EtsuChemical Co., Ltd.), 0.03 part by mass of dodecylmercaptan as a chaintransfer agent and 1.0 part by mass of a radical-polymerizablesurfactant “AQUARON HS-10” available from Dai-Ichi Kogyo Seiyaku Co.,Ltd., in 49 parts by mass of water, and a polymerization initiatorobtained by dissolving 0.3 part by mass of potassium persulfate in 9.7parts by mass of water. The resultant mixed solution was dropped throughthe dropping funnel into the polymerization flask for 3 hours, and thecontents of the flask were emulsion-polymerized at 80° C.

Thereafter, the resultant aqueous dispersion was aged at 80° C. for 2hours, cooled and then treated with aqueous ammonia for adjusting the pHthereof to 7.5 to thereby obtain an aqueous emulsion containingparticles having an average particle size of 150 nm. Further, 2 parts bymass of a silicone-based defoamer “BYK025” available from BYK-ChemieGmbH and 0.3 part by mass of an urethane-based thickening agent “EXP300”available from Rohm and Haas Company were added to the thus obtainedaqueous emulsion to obtain an acrylic emulsion-type adhesive.

(2) Production of Overlaminating Adhesive Film

A silicone release agent-coated polyethylene laminate-type release paperas a release material whose surface contacting with an adhesive layersubsequently formed thereon had a centerline average surface roughnessof 0.2 μm, was coated with the acrylic emulsion-type adhesive obtainedin the above step (1) by a knife coater to form the adhesive layerhaving a dried thickness of 20 μm. Then, a 25 μm-thick PET film waslaminated over the adhesive layer to prepare an overlaminating adhesivefilm (transfer coating method).

The thus obtained overlaminating adhesive film was tested to evaluatethe above properties thereof The results are shown in Table 1.

Example 2

The same procedure as in EXAMPLE 1 was repeated except thatγ-methacryloxypropyltriethoxysilane as an alkoxysilane group-containingunsaturated monomer (“Silicone KBE-503” available from Shin-EtsuChemical Co., Ltd.) was used insteadγ-methacryloxypropyltrimethoxysilane, to obtain an overlaminatingadhesive film. The results of evaluation of the thus obtained film areshown in Table 1.

Example 3

The same adhesive as prepared in the step (1) of EXAMPLE 1 was directlyapplied onto a 25 μm-thick PET film to form an adhesive layer having adried thickness of 20 μm. Then, the same release paper as used inEXAMPLE 1 was laminated over the adhesive layer to obtain anoverlaminating adhesive film (direct coating method). The results ofevaluation of the thus obtained film are shown in Table 1.

Comparative Examples 1 to 4

The same procedure as in EXAMPLE 1 was repeated except that compositionof the acrylic resin constituting the acrylic emulsion-type adhesive,average particle size and pH were changed as shown in Table 1, to obtainoverlaminating adhesive films. The results of evaluation of the thusobtained films are shown in Table 1.

Comparative Example 5

The same procedure as in EXAMPLE 1 was repeated except that aglassine-type release paper whose surface contacting with the adhesivelayer had a centerline average surface roughness of 0.7 μm, was used asthe release material, to obtain an overlaminating adhesive film. Theresults of evaluation of the thus obtained film are shown in Table 1.

Comparative Example 6

The same procedure as in EXAMPLE 3 was repeated except that aglassine-type release paper whose surface contacting with the adhesivelayer had a centerline average surface roughness of 0.7 μm, was used asthe release material, to obtain an overlaminating adhesive film. Theresults of evaluation of the thus obtained film are shown in Table 1.

TABLE 1 Com. Com. Com. Com. Com. Com. Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex. 2 Ex.3 Ex. 4 Ex. 5 Ex. 6 Adhesive 2EHA*¹ 80 80 80 80 80 80 80 80 80 MMA*² 1616 16 16 16 16 16 16 16 MAA*³ 2 2 2 2 2 2 2 2 2 AA*⁴ 2 2 2 — 2 2 2 2 22HEA*⁵ — — — 2 — — — — — Dodecylmercaptan 0.03 0.03 0.03 0.03 0.03 0.030.03 0.03 0.03 Silicone KBM-503 0.2 — 0.2 0.2 0.2 0.2 0.2 0.2 0.2Silicone KBE-503 — 0.2 — — — — — — — pH 7.5 7.5 7.5 7.5 7.5 9.0 6.8 7.57.5 Average particle 150 150 150 150 250 150 150 150 150 size (nm)Release paper Centerline average 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.7 0.7surface roughness (μm) Coating method T** T** D*** T** T** T** T** T**D*** Transparency Haze (%) 2.06 2.43 1.73 2.32 2.78 2.20 2.80 2.30 2.14Water whitening Haze (%) 3.65 4.30 2.63 3.88 11.0 3.45 10.8 4.86 4.30resistance Ink bleeding A A A C B C C C A resistance LaminatingTransparency due A A A C C B B C B suitability to bubbles Peel traceOrange peel (%) 88.5 87.2 92.8 77.5 78.2 86.8 88.0 65.5 67.5 Note:*¹2-ethylhexyl acrylate *²Methyl methacrylate *³Methacrylic acid*⁴Acrylic acid *⁵2-hydroxyethyl acrylate T**: Transfer coating methodD***: Direct coating method

As apparently understood from Table 1, the overlaminating adhesive filmsproduced according to the present invention (EXAMPLES 1 TO 3) were notonly excellent in all of transparency, water whitening resistance, inkbleeding resistance and laminating suitability, but also substantiallyfree from peel traces. On the other hand, the film using the monomercomponent containing the hydroxy-containing unsaturated monomer(COMPARATIVE EXAMPLE 1) as well as the films using the adhesive whose pHwas out of the specific range of the present invention (COMPARATIVEEXAMPLES 3 AND 4), were deteriorated in especially ink bleedingresistance. In addition, the film using the adhesive having an averageparticle size exceeding the specific range of the present invention(COMPARATIVE EXAMPLE 2) was deteriorated in especially water whiteningresistance, and the films using the release paper whose surface had acenterline average surface roughness exceeding the specific range of thepresent invention (COMPARATIVE EXAMPLES 5 AND 6) were deteriorated inespecially evaluation results of peel traces.

INDUSTRIAL APPLICABILITY

The overlaminating adhesive film of the present invention is excellentin not only orange peel resistance of its adhesive layer and waterresistance, but also bubble-removing property after being laminated toan adherend. Further, an ink-jet printed surface over which theoverlaminating adhesive film of the present invention is laminated,suffers from a less ink bleeding.

1. A method of making an overlaminating adhesive film, the methodcomprising producing an adhesive layer comprising a silicon-containingacrylic emulsion-type adhesive by a process comprisingemulsion-polymerizing a monomer component, which includes analkoxysilane group-containing unsaturated monomer in which each alkoxygroup has 1 to 4 carbon atoms, but which includes no hydroxy-containingunsaturated monomer, to form an aqueous dispersion; adjusting the pH ofthe aqueous dispersion to a range of from 7.2 to 8.5 to obtain anaqueous emulsion comprising the silicon-containing acrylic emulsion-typeadhesive, where the silicon-containing acrylic emulsion-type adhesivehas an average particle size of 200 nm or smaller; providing atransparent film and a release material; applying a coating of theaqueous emulsion onto either the transparent film or the releasematerial; and drying the coating; and laminating the transparent film,the adhesive layer and the release material to produce theoverlaminating adhesive film.
 2. The method according to claim 1,wherein the monomer component further includes an acrylic acid estercontaining a C₄ to C₁₂ alkyl group and a carboxyl-containing unsaturatedmonomer.
 3. The method according to claim 1, wherein the coating of theaqueous emulsion is applied on the transparent film, and then therelease material is laminated over the coating.
 4. The method accordingto claim 1, wherein the coating of the aqueous emulsion is applied onthe release material, and then the transparent film is laminated overthe coating.
 5. The method according to claim 1, wherein the transparentfilm is selected from the group consisting of polyolefin films andpolyester films.
 6. The method according to claim 1, wherein theoverlaminating adhesive film comprises 5 to 50 g/m² of thesilicon-containing acrylic emulsion-type adhesive, based on the driedweight of the silicon-containing acrylic emulsion-type adhesive.
 7. Themethod according to claim 1, wherein the monomer component comprises0.001 to 5 mass % of the alkoxysilane group-containing unsaturatedmonomer.
 8. The method according to claim 1, wherein thesilicon-containing acrylic emulsion-type adhesive comprises a polymerhaving a carbon-carbon backbone and containing alkoxysilane functionalgroups.
 9. The method according to claim 1, wherein thesilicon-containing acrylic emulsion-type adhesive has an averageparticle size of from 150 to 200 nm.
 10. The method according to claim1, further comprising producing the release material by applying asilicone-based release agent onto a resin film laminated on a kraftpaper, a glassine paper, a wood-free paper, a cast-coated paper or aclay-coated paper; or a water-soluble polymer coated on a kraft paper, awood-free paper or a cast-coated paper.
 11. The method according toclaim 1, wherein the coating of the aqueous emulsion is applied directlyto a surface of the release material; and the surface of the releasematerial has a centerline average surface roughness of 0.5 μm or lower.